Issue 35

Š. Major et alii, Frattura ed Integrità Strutturale, 35 (2016) 379-388; DOI: 10.3221/IGF-ESIS.35.43 381 treatment. In this work, specimens with two types of surface treatment and implants without surface treatment were used. The first surface treatment was based on deposition TiO 2 . The second deposition was based on TiN surface. The both screws with surface treatment have a higher surface roughness than a screw without surface treatment. Roughness of a screw without treatment is R a = 0.1 μm while roughnesses of the nitrided and TiO 2 covered screws are R a = 2.7 μm and R a = 3.1 μm. The rougher surface improves the reception of the material by bones. Fig. 1 show experimental determination of Paris law for titanium alloy Grade 23. Paris law can be written for this material as: 12 4.2 5.1 10 da K dN    (1) Also fatigue test were carried out, results of these experiments are shown in Fig. 2. This figure shows fatigue curve (stress to number of cycle) σ-N. Fatigue test were carried out by room temperature on cylindrical specimen with diameter 4 mm. Loading frequency of fatigue experiment was 50 Hz and the loading was full reserve R = −1. In Fig. 2 is clearly visible reduction of fatigue limit for both types of surface treatments. Figure 2 : Fatigue curves in Grade 23 titanium alloy with surface layer TiO 2 and TiN and without surface treatment. Figure 3 : Specimen used in fatigue tests.